This invention relates in general to universal joints, such as are commonly used in vehicular drive train systems. In particular, this invention relates to an improved structure for a cross for use in such a universal joint that includes a lubrication system for positively causing lubricant to flow from a central cavity through a lubrication passageway formed in a trunnion of the cross and into a region where bearings are contained within a bearing cup mounted on the trunnion.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a typical driveshaft assembly includes a hollow cylindrical driveshaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends thereof. The front end fitting forms a portion of a front universal joint that connects the output shaft of the engine/transmission assembly to the front end of the driveshaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint that connects the rear end of the driveshaft tube to the input shaft of the axle assembly. The front and rear universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.
Each of the universal joints typically includes a cross having a central body portion with four cylindrical trunnions extending outwardly therefrom. The trunnions are oriented in a single plane and extend at right angles relative to one another. A hollow cylindrical bearing cup is mounted on the end of each of the trunnions. Needle bearings or other friction-reducing structures are provided between the outer cylindrical surfaces of the trunnions and the inner cylindrical surfaces of the bearing cups to permit rotational movement of the bearing cups relative to the trunnions during operation of the universal joint. In the front universal joint of the above-described driveshaft assembly, the bearing cups supported on the first opposed pair of the trunnions on a front cross are connected to the front end fitting of the driveshaft assembly, while the bearing cups supported on the second opposed pair of the trunnions on the front cross are connected to an end fitting secured to the output shaft of the engine/transmission assembly. Similarly, in the rear universal joint of the above-described driveshaft assembly, the bearing cups supported on the first opposed pair of the trunnions on a rear cross are connected to the rear end fitting of the driveshaft assembly, while the bearing cups supported on the second opposed pair of the trunnions on the rear cross are connected to an end fitting secured to the input shaft of the axle assembly.
In order to insure proper operation of the universal joint, lubricant is usually provided in the regions where the bearings are provided between the outer cylindrical surfaces of the trunnions and the inner cylindrical surfaces of the bearing cups. To accomplish this, the central body portion of the cross can have an internal cavity formed therein that communicates with respective lubricant passageways that are formed through each of the trunnions. A lubricant fitting is provided on the central body portion of the cross to allow lubricant to be injected therethrough under pressure into the internal cavity. During this injection, the lubricant flows through the lubrication fitting into the cavity, radially outwardly from the cavity through each of the lubricant passageways, laterally around the ends of each of the trunnions, and radially inwardly into the regions of the bearings. A seal and dust guard assembly may be provided about the open end of each of the bearing cups to retain the lubricant in the regions of the bearings and to prevent the entry of dirt, water, and other contaminants therein.
Although this structure has been effective, it is a static lubrication system, and no mechanism is provided for positively causing the lubricant to flow through into the regions of the bearings after the initial injection. In many instances, this results in the need for periodic re-lubrication of the cross, even through a quantity of the lubricant may still be present within cavity and some or all of the lubricant passageways. Accordingly, it would be desirable to provide an improved structure for a cross for use in a universal joint that includes a lubrication system for positively causing lubricant to flow through from the cavity through the lubricant passageways and into the regions of the bearings.